Grain size dependence of electroplastic effect in NaCl

The influence of a dc electric field 1-3 kV cm(-1) on the flow stress of ex truded polycrystalline (d(0) = 30 mu m) 99.9%NaCl was determined in compres sion at 23-532 degrees C and the results compared with those obtained previ ously on coarse grained (d(0) = 2 mm) cast material. The field significantl y decreased the pow stress in both materials; the effect increased with ele ctric field and with strain, but varied with temperature, being a maximum a t approximately 100 degrees C below the brittle to ductile transition tempe rature without field. The change in flow stress when the field was alternat ely turned 'on' and 'off' during the course of a test was about an order of magnitude lower, than when the field was applied continuously. The electri c field had no detectable effect on the apparent activation volume v, nor o n the stress exponent n for plastic pow. The temperature dependence of the effect of grain size on the reduction in pow stress by the electric field w as related to the effect of grain size on the brittle to ductile transition temperature. The present results are in accord with the earlier conclusion for the cast material that the major effect of the field is to enhance cro ss-slip. BCT/297. (C) 1998 The Institute of Materials.